In the case of liver tumors (or also in the case of HCC=hepatocellular carcinoma or corresponding metastases) ablation therapy is a form of treatment which is becoming increasingly important in the medical field, especially for small cell liver tumors. The reason for this is firstly the interventional nature of this type of action (in contrast to resection, the complication rate is significantly lower, among other things) and secondly the improved mortality tables. This means that ablation therapy exhibits significant advantages compared to resection of the liver. The result of the ablation therapy mainly depends on two factors:
1. Size of the Liver Tumor/Metastasis:
If the longitudinal axis (longest axis of the tumor ellipsoid) is less than xmax (Xmax typically at approx. 3 cm), optimal conditions obtain for ablation therapy using RF (radio frequency). This size is typically measured on the basis of volume data from imaging modalities (e.g. CT, MR, rotational angiography). The stipulated limit of approx. 3 cm applies for RF ablations; microwave ablations or ablations using electro-perforations are potentially also able to treat somewhat larger tumors/metastases successfully.
It should be added here that that it does not always make sense to make the limit of the tumors which are treated using ablation therapy dependent on the longest axis of the tumor ellipsoid. It would be advantageous to determine the true volume (in mm3) of the tumor.
2. Vascularity of the Tumor/Metastasis:
RF ablation works with heat. In other words, one (or more than one) needle is inserted into the tumor tissue, and the surrounding tissue is in practice “cooked” (heated until the cells die) by applying a high frequency. In order to “cook” the cells, a minimum temperature must be reached. Depending on the distance of the RF point different cell temperatures are reached; in other words, the further a cell is from the ablation point hotspot (point of maximum heat), the lower the probability that enough energy is yet available at this point (in the form of temperature) to “cook” this cell. It is clear from this explanation that only tumors up to a particular maximum size can be treated using RF ablation. If there are vessels in the immediate vicinity of the tumor to be ablated (e.g. main branches of the liver arteries), these vessels—if they are of a certain minimum size—have a cooling effect. This “vessel cooling” works counter to the desired ablation effect (=heat). In order nevertheless to achieve an ablation effect of the desired size (cf. 3 cm longitudinal axis) these vessels are “eliminated”. With smaller, less important vessels this is done by embolization; with larger vessels, which mainly serve to supply the vessels in healthy tissue, this is done by short-time occlusion (e.g. balloon occlusion). The aim with both procedures is to reduce or eliminate the cooling of the tumor tissue, in order to ablate/“cook” a maximally large area.
In the current clinical environment the size of a tumor is determined on the basis of the longitudinal axis methods described above. The vascularity of the tumor is only very rarely examined and taken into account.
This procedure has two major disadvantages:                The longitudinal axis method is thus used because for regular (e.g. spherical) tumors it represents a good approximation for the volume of the tumor. An exact measurement of the volume of the tumor is not really possible, or else is associated with a great deal of manual work for the physician. This means that generally a measurement of the volume is dispensed with. A simple and fast way of measuring the volume of the tumor (in addition to determining the longitudinal axis) would be desirable for the physician, because this would enable him to reach a more accurate decision as to whether the tumor in question can be treated by ablation therapy, or whether a resection is necessary.        Paying little or no attention to the vascularity of the tumor means that the area of the cooked cells is sometimes significantly overestimated. Thus there exists the risk that large parts of the tumor cells are not killed, and the anticipated effect (e.g. the elimination of the entire tumor) is not achieved. Thus there exists the risk of subjecting the patient to an intervention without the anticipated and desired benefit.        
A simple and fast statement about the vascularity of the tumor would be desirable for the physician because it would then be possible for him (if necessary) to occlude or embolize the corresponding vessels beforehand, and thus ensure the success of the therapy.